(1) Field of the Invention
The present invention relates to a pellicle structure and a process for the preparation thereof. More particularly, the present invention relates to a pellicle structure in which a pellicle film shows excellent performance and the pellicle film has a sufficient bonding strength to a frame, and a process for the preparation thereof.
(2) Description of the Related Art
In the production of integrated circuits such as IC and LSI, a pellicle is attached to a photomask or reticle used for forming a circuit pattern on a semiconductor substrate so that projection of the shadow of a foreign substance such as dust bonded to the pattern to be light-exposed, or to the photomask or reticle, on the pattern at the light exposure, can be prevented.
The conventional pellicle comprises a pellicle film composed of nitrocellulose or the like and a frame composed of aluminum or the like, at an upper part of which the pellicle film is spread. If the pellicle is used in a manner covering the photomask or reticle, the above-mentioned adhesion of a foreign substance to a photomask or reticle can be prevented. However, if a foreign substance is present on the pellicle film, the image of the foreign substance projected at the light exposure is not focused on the pellicle film but forms a so-called fuzzy image. Accordingly, bad influences by a foreign substance can be eliminated.
Coating layers such as an adhesive layer for preventing adhesion of an intruding foreign substance to a photomask or reticle, a reflection-preventing layer for preventing reduction of the exposure light quantity by reflection of the exposure light and an adhesive reflection-preventing layers exerting both the functions are formed in pellicles or on the inner faces of frames. However, if a pellicle film having such a coating layer is bonded to a frame, there arises a problem of reduction of the bonding strength.
In general, after a coating layer such as the above-mentioned adhesive reflection-preventing coating layer or nonadhesive reflection-preventing coating layer is formed on the entire surface of the pellicle film by spin coating or the like, a pellicle is fabricated by bonding the pellicle film to a frame by using an adhesive.
If the pellicle film having a coating layer such as a reflection-preventing layer is directly bonded to a frame as in the conventional technique, the bonding strength is low, and therefore, at the air-blowing operation conducted for removing a foreign substance from the surface of the pellicle film, the pellicle film is peeled from the frame.